Generally, an oil pump of an internal combustion engine circulates engine oil under pressure to engine components, such as rotating bearings, sliding pistons, camshaft, and the like to reduce friction between the components while the engine is running, thereby providing smooth engine operation.
Recently, technology for reducing friction between engine components and improving fuel efficiency has been developed, while the engine is running using a low friction mechanism such as continuously variable valve timing (CVVT) and continuously variable lift (CVVL).
In particular, a directly-connected type engine oil pump in which an oil pump of an internal combustion engine is directly connected to a crankshaft has been used to reduce friction, and thus improve fuel efficiency and reduce cost in comparison to an indirectly connected engine oil pump that is driven by a chain connected to a crankshaft.
In a conventional oil pump, as shown in FIG. 1, an inner rotor 5 and an outer rotor 7 are provided at a center of a pump housing 10 where an intake port 1 and a discharging port 3 are provided. The oil within an oil fan is drawn into the pump housing by negative pressure caused by a volume change when the inner rotor 5 and the outer rotor 7 rotate. The oil that is drawn in is compressed to a high pressure and then discharged to the discharging port due to a volume change, and then provided to engine components.
The oil pressure in the oil pump of the engine, which is discharged, increases in proportion to the number of engine reciprocation. When the oil pressure increases excessively durability of the engine components may be degraded. A relief valve 9 is provided on the oil pump to prevent this excessive increase of the oil pressure, and the oil is bypassed when the relief valve 9 is opened in accordance with the oil pressure.
In the related art, an excessively large amount of oil flow is bypassed instantly due to the excessive oil pressure when the relief valve 9 operates, and thus, the discharge pressure of the oil increases to induce resonance of the relief valve.
In addition, the oil within the engine oil pump may leak when the oil pump is not operated for a long time, thus generating resonance in the relief valve when it initially starts.
The description provided above as a related art of the present disclosure is just for helping in understanding the background of the present disclosure and should not be construed as being included in the related art known by those skilled in the art.